What might have turned dupliverts off?
Ok I have no idea what is going on, but I played with your blend file and got it to work again. It must be some kind of bug.


Collapse your windows on the left like I did
Then Collapse your side window with your main 3D window
Click the bottom window pane to get back to your 3D view
Notice it changes what layer you are on at the bottom
Click back to the 2nd layer with your object on it
And all of a sudden dupliverts started working again. 


WEIRD!!